Changes in free radicals system of Cladosporium cladosporioides-melanin and model DOPA-melanin caused by diamagnetic Cd2+ ions were studied by electron paramagnetic resonance (EPR) spectroscopy. EPR line of eumelanin was mainly found in the spectrum of Cl.cl.-melanin. Cd2+ ions increased o-semiquinone free radicals concentration in both natural and synthetic melanins. Cd2+ broadened EPR lines of Cl.cl.-melanin in mycelium and the ions fastened spin-lattice relaxation processes. The narrower EPR lines and slower spin-lattice relaxation were obtained for DOPA-melanin-Cd2+ complexes than for DOPA-melanin. Pheomelanin additionally existing in Cl.cl. samples was responsible for differences between the EPR data for Cl.cl. melanin and DOPA-melanin. (C) 2004 Elsevier B.V. All rights reserved.